System Bits: Feb. 23

Making electrons act like liquid
While electrical resistance is a simple concept in that rather like friction slowing down an object rolling on a surface, resistance slows the flow of electrons through a conductive material, and now, MIT professor of physics Leonid Levitov and Gregory Falkovich, a professor at Israel’s Weizmann Institute of Science have found that electrons can sometimes turn resistance on its head to produce vortices and backward flow of electric current.

The prediction of “negative resistance” is just one of a set of counterintuitive and bizarre fluid-like effects encountered under certain exotic circumstances, involving systems of strongly interacting particles in a sheet of graphene, a two-dimensional form of carbon.

New work shows that interactions of electrons in graphene lead to viscous current flows, creating tiny whirlpools that cause electrons to travel in the direction opposite to the applied voltage — in direct violation of standard electrical theory. White lines show current streamlines, colors show electrical potential, and green arrows show the direction of current, for viscous (top) and normal (ohmic) flows. (Source: MIT)

And given that graphene is increasingly being used in a variety of applications, electronic engineers cannot really utilize the material without an understanding of its electronic properties, and whether the electrons move like bullets or swim in treacle creating whirlpools obviously makes a huge difference, the researchers said.

Portable device for rapid, highly-sensitive diagnostics
To address the need for portable diagnostic medical equipment especially in remote regions with limited health facilities experiencing an epidemic, EPFL researchers have developed a low-cost and portable microfluidic diagnostic device, already tested on Ebola and can be used to detect many other diseases.

The researchers reminded that over the past several years, microfluidic devices have shown extraordinary potential in the area of diagnostics. They are composed of silicone rubber with minuscule channels the width of a hair and can rapidly detect a number of different biomarkers in very small quantities of blood.

A portable and low-cost diagnostic device has been developed at EPFL. This microfluidic tool, which has been tested with Ebola, requires no bulky equipment. It is thus ideally suited for use in remote regions. (Source: EPFL)

The EPFL microfluidic platform is portable, runs on battery power and is completely self-sustained. It operates seamlessly with inexpensive microscopes and provides very high levels of accuracy and detection. The platform can quantify up to 16 different molecules – or biomarkers – in a tiny amount of blood (less than 0.005 milliliters). The device is unique in that it is composed of both analog and digital detection mechanisms, while conventional devices had only integrated one or the other. Digital detection is highly sensitive and can detect the presence of a single biomarker. However, it is less effective when the concentration of biomarkers is too high, due to signal saturation. Analog measurements, on the other hand, function best at higher biomarker concentrations. Using these two detection mechanisms simultaneously, the composition of a drop of blood can be thoroughly analyzed in a short amount of time. The analysis provides precious medical information: it could help doctors make an early diagnosis or determine the stage of a disease.

Interestingly, the researchers also found they could load the blood sample directly onto the device and perform on-chip biomarker quantitation without requiring any sample pre-treatment, which would typically require centrifuges, large volume samples and a long processing time.

Bioelectronics trailblazer
While at a technical university in Berlin, Polish-born Monika Weber was the only woman in her electrical engineering class but today, the Yale Ph.D. candidate is blazing a trail in bioelectronics with a product she believes can change the world.

She founded the Yale University-startup Fluid-Screen, which has developed the world’s first portable biosensor capable of detecting bacteria in water and blood — quickly and cheaply.

Monika Weber founded Fluid-Screen, a Yale University startup that has developed a portable biosensor capable of detecting bacteria in water quickly and cheaply. (Source: Yale University)

The device will be tested on Hudson River water this spring in a partnership with with Riverkeeper, a New York-based advocacy group.

The Fluid-Screen device — about the size of a quarter — uses ultra tiny nanosensors capable of detecting low concentrations of biomolecules, or disease markers, in water and blood in less than 30 minutes.

The technology, which is awaiting a patent, is based on a silicon biosensor chip developed at Yale under the guidance of Prof. Mark A. Reed, a physicist and associate director of the university’s Institute of Nanoscience and Quantum Engineering.

Fluid-Screen is targeted for detecting pathogens in water for quality screening, and for blood for bacterial infection, whereas existing methods either take too long — 24 hours or more — or are too expensive and not portable. Fluid-Screen’s goal is to make it quick and inexpensive.